Ocean may store far less carbon than we hoped

(ORDO NEWS) —  The oceans are one of the most important carbon sinks on our planet. They currently store about 39,000 gigatons of carbon dioxide – 50 times more than what is currently circulating in the atmosphere.

However, we cannot rely on carbon capture and storage to solve the climate crisis because we are producing too much excess CO2 too quickly.

What’s more, a new study shows that the deep ocean is not capable of holding as much carbon as previously thought.

The scientists looked at the carbon cycle that is sucked up by microscopic plants that live near the surface of the water and then drifts down to the seafloor.

Based on new particle tracking models, it appears that the process is “leaky” and retains less carbon over the long term than previously thought.

“The ocean is an important carbon sink, and the depth to which biological carbon settles affects how much atmospheric carbon dioxide the ocean stores,” says Chelsea Baker, ocean biogeochemistry model analyst at the UK’s National Oceanographic Centre.

“In this study, we show that the longevity of carbon storage in the deep ocean may be significantly less than commonly believed.”

Carbon must be stored for 100 years to be on a climate-relevant time scale.

Until now, it was believed that the circulation paths of the deep ocean would keep every particle of trapped carbon that reached a depth of 1,000 meters (3,250 feet) away from the world for several millennia.

Modeling used by the researchers showed that only an average of 66 percent of the carbon that reached depths of 1,000 meters (3,250 feet) in the North Atlantic would be stored for a century or more.

Although the efficiency of CO2 capture varied depending on factors including ocean currents and temperature, the carbon would have to reach depths of 2,000 meters (6,500 feet) to almost certainly persist for more than 100 years at that depth, 94 percent of the carbon remained in place for a century or more, simulations showed.

“These results have implications for estimates of future predictions of carbon uptake by global biogeochemical models, which may be overestimated, and for carbon management strategies,” the researchers write in their published paper.

As the climate and the ocean change, the models will need to be updated. Experts believe that in the future, the oceans will become more stratified as they warm, which means less mixing between layers – and less carbon sinking to the bottom.

And the more accurate our models are, the better we’ll be able to understand what’s in store for us, and how we can prevent it, if need be. Scientists need to know, as accurately as possible, how much CO2 we produce, how much the ocean can store, and how long it will last.

It is possible that by supplementing the natural carbon cycle in various ways, more carbon can be removed from the atmospheric circulation – but for this we need to know how efficient and effective the deep ocean is as a carbon sink.

“Our findings may be important as artificially increasing ocean carbon sequestration is one of the avenues being explored to help us reach net zero by 2050. For example, through ocean carbon removal schemes such as iron fertilization,” Baker says.

“The effectiveness of such natural solutions often depends on the assumption that carbon trapped in the deep ocean will be stored for hundreds of years, and our work shows that things may not be that simple.”

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